:root {
    --primary: #2563eb;
    --secondary: #64748b;
    --success: #10b981;
    --danger: #ef4444;
    --background: #f8fafc;
    --surface: #ffffff;
    --text: #1e293b;
    --border: #e2e8f0;
}

[data-theme="dark"] {
    --background: #0f172a;
    --surface: #1e293b;
    --text: #f1f5f9;
    --border: #334155;
}

* { box-sizing: border-box; margin: 0; padding: 0; }

:focus-visible {
    outline: 3px solid #4A90D9;
    outline-offset: 2px;
}

button:focus-visible,
a:focus-visible {
    outline: 3px solid #4A90D9;
    outline-offset: 2px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--background);
    color: var(--text);
    min-height: 100vh;
}

.app-container {
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

.app-header {
    background: var(--primary);
    color: white;
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.app-header h1 { font-size: 1.5rem; }
.app-header .subtitle { opacity: 0.9; font-size: 0.875rem; }

.main-nav {
    background: var(--surface);
    border-bottom: 1px solid var(--border);
    display: flex;
    gap: 0.5rem;
    padding: 0.5rem 2rem;
}

.nav-btn {
    padding: 0.75rem 1.5rem;
    border: none;
    background: transparent;
    cursor: pointer;
    border-radius: 0.5rem;
    transition: all 0.2s;
    color: var(--text);
}

.nav-btn:hover { background: var(--background); }
.nav-btn.active { background: var(--primary); color: white; }
.nav-btn:focus-visible {
    outline: 3px solid #4A90D9;
    outline-offset: 2px;
}

.main-content {
    flex: 1;
    padding: 2rem;
}

.content-section { display: none; }
.content-section.active { display: block; }

.login-container {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 60vh;
}

.login-card {
    background: var(--surface);
    padding: 2rem;
    border-radius: 1rem;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
    width: 100%;
    max-width: 400px;
    text-align: center;
}

.login-card h2 { margin-bottom: 1rem; }

.form-group {
    margin-bottom: 1rem;
    text-align: left;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
}

.form-group input,
.form-group select {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border);
    border-radius: 0.5rem;
    font-size: 1rem;
    background: var(--surface);
    color: var(--text);
}

.form-group input:focus-visible,
.form-group select:focus-visible {
    outline: 3px solid #4A90D9;
    outline-offset: 2px;
    border-color: var(--primary);
}

.btn-primary {
    background: var(--primary);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: 0.5rem;
    cursor: pointer;
    font-size: 1rem;
    width: 100%;
    transition: opacity 0.2s;
}

.btn-primary:hover { opacity: 0.9; }
.btn-primary:focus-visible {
    outline: 3px solid #ffffff;
    outline-offset: 2px;
}

.privacy-notice {
    margin-top: 1rem;
    font-size: 0.875rem;
    color: var(--secondary);
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
    margin-top: 1.5rem;
}

.stat-card {
    background: var(--surface);
    padding: 1.5rem;
    border-radius: 0.75rem;
    text-align: center;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}

.stat-card h3 {
    font-size: 2rem;
    color: var(--primary);
}

.app-footer {
    background: var(--surface);
    border-top: 1px solid var(--border);
    padding: 1rem;
    text-align: center;
    font-size: 0.875rem;
    color: var(--secondary);
}

@media (max-width: 768px) {
    .main-nav { flex-wrap: wrap; }
    .nav-btn { flex: 1; text-align: center; }
}